Chinese Academy Of Geological Sciences Doctorate Dissertation

The salt lakes in Tibet plateau are rich in Li,B,Rb and Cs.But none of soudium sulfate subtype salt lakes in Tibet was carried on lithium development,due to the high Mg/Li ratio,bad traffic and energy conditions of these lakes.The Laguocuo Salt Lake is located on the northern Tibetan Plateau,in Ge^rze^ County under the jurisdiction of the Ngari Prefecture of the Tibet Autonomous Region.The brine of Laguocuo Salt Lake is sodium sulfate subtype,and rich in K,Li,B,Rb and Cs.It has been preliminarily estimated that Laguocuo Salt Lake’s lithium reserves have reached the magnitude of a large lithium brine deposit（>5×105t）.Considering the bad exploitation conditions,the development and utilization of brine lithium resource in Laguocuo must rely on salt lake’s local conditions and local materials.Therefore,a series experiment of evaporation and brine mixing were performed to provide the basic date for the future development of Laguocuo Salt Lake.An evaporation experiment of the summer brine from the Laguocuo Salt Lake at a daily average temperature of 17℃ was firstly conducted in this thesis.The results showed that SO42-was greatly concentrated,and lithium was precipitated dispersedly as lithium double salt（Li2SO4₃Na2SO4₁2H2O）in the early stage of the evaporation process.Before lithium salts precipitated,the highest concentration of lithium in the residual liquor was only 2.07 g·L-1,lithium enrichment for future separation and extraction was difficult.As the winter and spring climate of Laguocuo Salt Lake area is very cold,a new development technology of precipitation mirabilite to enrichment lithium in low temperature evaporation was first proposed to avoid the early precipitation of lithium double salt.Therefore,we performed a 273.15 K-isothermal evaporation experiment on summer brine and a 278 K-isothermal evaporation experiment on autum brine,to reveal the enrichment behavior of lithium in the brine,the salt precipitation sequence and evaporation-crystallization path of the brine.The results show that large amounts of SO42can be precipitated as mirabilite in the initial stage of the evaporation process,thus lowering the SO42-concentration in the residual brine,avoiding the early precipitation of lithium double salt,as result Li+was effectively concentrating in the residual brine in low temperature evaporation process（the highest Li+ concentration respectively reach 27.75 g·L-1 and 22.32 g·L-1）.And the enrichment behavior of lithium is firstly described as a power function of Y=k（1-X）-1,where Y=the concentration of lithium in the residual brine,X=the extent of evaporation,and k=the initial value of lithium concentration of the brine.It suggest that lower temperature is benefical to lithium enrichment in sodium sulfate subtype’s brine evaporation.The experiment suggests that the salts precipitated from the brine contain not only the mineral assemblage with the characteristics of carbonate-type salt lakes,such as borax and lansfordite,but also the mineral assemblage with the characteristics of sulfate-type salt lakes,such as carnallite and lithium sulfate monohydrate.This finding with the data from the Zhabei Salt Lake’s brine in 1978 and the distribution characteristics of the hydrochemical zones of salt lakes on the Qinghai-Tibet Plateau,indicate that this salt lake is in a special stage of transition from a sulfate-type salt lake to a carbonate-type.Laguocuo salt lake is nearby carbonate type salt lake Zabuye,CO32--rich brine is available for Laguocuo lithium exploration.Therefore,"sodium sulfate subtype and carbonate type salt lake combined development",the other new methods of lithium concentrated by summer and autumn higher-temperature natural evaporation,and lithium carbonate recovery from natural brine by brine mixing and lithium precipitation were presented in this thesis.The lithium-rich brine that gained by summer natural evaporation of brine from Laguocuo salt lake was removed magnesium and sulfate by quicklime（CaO）.Furthermore,the low-Mg2+and SO42-brine was concentrated by natural evaporation（average temperature 17℃）and high-lithium brine was collected with Li+concentration is 16.20 g·L-1.Finally,the lithium carbonate recovery was carried out thorough high-lithium Laguocuo brine mixed with high-carbonate Zhabuye Caka brine,and the effect of mixing ratio of brine and precipitation temperature on the Li2CO3 contents of the precipitated mixing salts and lithium extraction percent in the mixing and precipitation process were investigated in this paper.The results show that brine mixing ratio is 1.75 and the precipitation temperature is 90℃ were the optimum operation conditions of lithium carbonate recovery,and the maximum lithium extraction percent and the maximum content of Li2CO3 in precipitates were reached to 82.66%and 88.25%,respectively.The higher purity Li2CO3 powder（>99.8%）was prepared by hot water leaching to dissolve NaCl and KCl from the precipitate.The result of XRD and SEM showed that the Li2CO3 powder was Zhabuyelite crystal,the particles of the powders were 1-5 μm sized prism or tablet shape with better disperse character and large surface area.